For production of non-amino organic acids including succinic acid by fermentation, usually, anaerobic bacteria such as those belonging to the genus Anaerobiospirillum or Actinobacillus are used (Patent Document 1 or 2, and Non-Patent Document 1). The use of anaerobic bacteria makes the yield of products high, while such bacteria require many nutrients for proliferation and therefore, there is a need for adding a large amount of organic nitrogen sources such as corn steep liquor (CSL) to a medium. The addition of abundant amounts of organic nitrogen sources not only leads to an increase in cost of the medium but also leads to an increase in cost of purification for isolating the product, which is uneconomical.
Furthermore, a method, which comprises culturing aerobic bacteria such as coryneform bacteria under an aerobic condition to proliferate bacterial cells and then collecting and washing the cells to use them as resting bacteria to produce succinic acid without oxygen aeration, has been known (Patent Document 3 and 4). This method is economical because the bacterial cells can grow sufficiently in a simple medium, into which a small amount of organic nitrogen is added for proliferation of bacterial cells, but this method is still to be improved in terms of the amount of generated succinic acid, the concentration thereof, and the production rate thereof per bacterial cells as well as simplification of production process, and the like.
Furthermore, when aerobic bacteria such as coryneform bacteria are cultured under oxygen-limited conditions, organic acids other than a desired substance such as lactic acid and acetic acid are excessively accumulated as by-products, resulting in suppressed growth of bacterial cells and significantly decreased productivity in fermentation. In addition, excessive amounts of counterions to neutralize the organic acids generated as by-products are required, thereby resulting in being uneconomical. To solve such problems, reduction in lactate generated as a by-product has been performed by using a coryneform bacterium having a reduced lactate dehydrogenase activity (Patent Document 5).
Even if the above-mentioned coryneform bacterium having a reduced lactate dehydrogenase activity is used, a large amount of acetic acid is generated as a by-product. As means for achieving the reduction of acetic acid in a culture medium, there have been known a method of enhancing expression of an acetic acid assimilating gene (aceP) in a bacterium belonging to the genus Escherichia (Patent Document 6), a method of enhancing expression of a gene encoding ACE protein in a bacterium belonging to the genus Escherichia (Patent Document 7), and the like. Those methods are intended to reduce generation of acetic acid as a by-product by actively assimilating acetic acid released into a culture medium. Meanwhile, as methods of suppressing generation of acetic acid as a by-product by suppressing the biosynthesis of acetic acid, there have been known a method of producing succinic acid using Escherichia coli in which phosphoacetyltransferase (pta) and lactate dehydrogenase (ldh) are deficient (Patent Document 8), a method of producing an amino acid using an enterobacterium in which pyruvate oxidase (poxB) is deficient, and a method of producing D-pantothenic acid using an enterobacterium in which pyruvate oxidase (poxB) is deficient (Patent Document 9).
As enzymes responsible for assimilation of acetic acid in coryneform bacteria, there have been reported acetate kinase (ack) and phosphotransacetylase (pta) (Non-Patent Document 2). On the other hand, it is assumed that not only the above-mentioned enzymes but also a plurality of enzymes such as pyruvate oxidase (poxB) (Patent Document 10), acylphosphatase (acp), aldehyde dehydrogenase, and acetyl-CoA hydrolase are responsible for generation of acetic acid, but a specific enzyme that contributes to the synthesis of acetic acid has not been clarified. Therefore, there has not been known a method of producing succinic acid using a strain of a coryneform bacterium having a decreased acetic acid biosynthetic enzyme.
Acetyl-CoA hydrolase is an enzyme to generate acetic acid from acetyl-CoA and water (3.1.2.1) and the gene sequence in Corynebacterium glutamicum has been predicted (Patent Document 11). However, no report has been provided for cloning of the gene and expression analysis of the gene, and its actual function has not been clarified.    Patent Document 1: U.S. Pat. No. 5,143,833    Patent Document 2: U.S. Pat. No. 5,504,004    Patent Document 3: JP11-113588A    Patent Document 4: JP11-196888A    Patent Document 5: JP11-206385A    Patent Document 6: JP06-14781A    Patent Document 7: JP07-67683A    Patent Document 8: WO 99/06532    Patent Document 9: WO 02/36797    Patent Document 10: EP1096013A    Patent Document 11: EP1108790A    Non-Patent Document 1: International Journal of Systematic Bacteriology, vol. 49, p 207-216, 1999    Non-Patent Document 2: Microbiology. 1999, February; 145 (Pt 2): 503-13